Improving the modelling of surface convection during natural night ventilation in building energy simulation models

The performance of night ventilation to cool buildings is highly sensitive to the convective surface heat flux. As a result, simulations in BES-models may largely over- or underestimate the real cooling potential of this technique. To assess this, a series of transient 2D CFD-simulations, including thermal mass in floor and ceiling, are made with variation on ACH, inlet temperature and inlet location. It is shown that the location of the inlet strongly influences the surface averaged convective surface heat transfer coefficients at the ceiling. The prediction of the transition from forced to natural convection is important. It is shown that the dimensionless Richardson number at the inlet could be a good indicator.